This invention relates to a connection method and structure for connecting covered wires with each other or connecting a covered wire to another member.
As a conventional connection structure for this kind of covered wires, a design proposed by this inventor (see Japanese Laid-Open Patent Application No. 7-320842) will be described.
For connecting two covered wires the outer periphery of which is coated with a cover portion made of resin, at their intermediate connection portions, a pair of resin chips which are of resin material, a horn for producing ultrasonic vibration, and an anvil for supporting the covered wires and resin chips at the time of connection are utilized. The anvil includes a base stand and a support portion projecting from the base stand. The support portion is designed in a substantially cylindrical shape. The support portion has a bore portion which is opened at the opposite side to the base stand side. Two-pairs of grooves are formed on the peripheral wall of the support portion so as to cross with each other substantially at the center of the bore portion. The four grooves are formed so as to open on the same side as the bore portion, extending along the projection direction of the support portion and intercommunicate with one another through the bore portion.
The pair of resin chips are designed in a disc shape having a slightly smaller outer diameter than the diameter of the bore portion of the anvil. Furthermore, an end face of a head portion of the horn is designed in a disc shape having an outer diameter which is substantially equal to or slightly smaller than that of the resin chips.
In order to connect the two covered wires to each other, both of the covered wires are overlapped with each other at the overlapping portions thereof and the overlapped connection portions are pinched by the pair of resin chips from the upper and lower sides of the connection portions. Specifically, one of the resin chips (the resin chip at the lower side) is inserted into the bore portion of the anvil such that the melting surface thereof is directed upward. Then, one covered wire is inserted into the pair of confronting grooves from the upper side of the inserted resin chip. Then, the other covered wire is inserted into the other pair of the confronting grooves. Finally, the other (upper side) resin chip is inserted such that the melting surface is directed downward. The covered wires are arranged in the bore portion so that the respective connection portions thereof cross each other at the center of the bore portion. Through this arrangement, the connection portions of the covered wires are pinched substantially at the center of the melting surfaces of the upper and lower resin chips respectively in the overlapping direction.
Subsequently, the cover portions at the connection portions of the covered wires are melted so as to be dispersed by ultrasonic vibration. Furthermore, the conductive wire portions (core) of the covered wires are conductively contacted with each other at the overlapping portions by pressing the covered wires from the outside of the resin chips. Thereafter, the pair of the resin chips are mutually melt-fixed at the melting surfaces to seal the overlapping portions.
Specifically, the head portion of the horn is inserted into the bore portion from the upper side of the finally-inserted upper (other) resin chip and placed on the upper resin chip to excite and press the connection portions of the covered wires from the outside of the upper and lower resin chips between the horn and the anvil. The cover portions are first melted and the conductive wire portions of the covered wires are exposed at the overlapping portions between the resin chips. At this time, the melted cover portions are extruded from the center side of the resin chips toward the outside thereof because the connection portions are pressed from the upper and lower sides, so that the conductive wire portions are more excellently exposed and surely conductively contacted with each other. Like the press direction, the direction of the excitation of the connection portions is set to be coincident with the overlapping direction of the covered wires, so that the action of extruding the melted cover portions from the center side of the resin chips to the outside thereof is promoted.
When the pressing and exciting operation on the connection portions is further continued after the melting of the cover portions, the resin chips are melted and the confronting melting surfaces of the resin chips are melt-fixed to each other. In addition, the outer peripheral surface portions of the cover portions which are adjacent to the conductively contacted conductive wire portions and the resin chips are melt-fixed. With this operation, the outer peripheral portions of the conductively-contacted conductive wire portions are kept to be coated with the resin chips.
However, in the connection structure described above, melted resin which flows out of a gap between the melting surfaces and when the resin chips are melted flows into groove portions so that it is hardened. At this time, downstream portions of the covered wires are near or in contact with bottoms of the groove portions. There are not sufficient spaces formed to allow melted resin to flow therein and this accompanied by increase of the amount of flow out, causes the melted resin to be deposited upstream of the covered wires (opening sides of the groove portions). Thus, if the cover portions are melted by high temperature melted resin, conductive wire portions are covered with the melted resin upstream of the covered wires where the melted resin is deposited, but not downstream where the melted resin is difficult to be deposited, the conductive wire portion remains exposed after the cover portions are melted. As a result, there may occur through holes which go through the cover portion or the conductive wire portion may remain exposed. If the conductive wire portions remain exposed, water or the like entering the connection portions in the resin chips may corrode the conductive wire portions, thereby inducing an increase in electric resistance. Further, due to a difference in pressure between the inside and outside of the covered wire, water or the like entering the inside of the covered wire 1 may reach a connector or the like provided on a side opposite to the overlapping portion S of the covered wire 1 thereby inducing a shortcircuit.
Thus, it is necessary to limit the pressing and excitation force by the horn in order to suppress the amount of flow out of the melted resin. However, it was difficult to achieve enhancement of the melting force between the resin chips and improvement of the covering performance of the conductive wire portion by the resin chips at the same time.